Composite material leaf springs are known, which springs typically comprise a filler material, for example glass roving or other filamentary solids, in an organic solid such as thermoplastic or thermosetting plastic. Such springs are shown, for example, in U.S. Pat. Nos. 2,600,843; 2,829,881 and 3,142,598. Known methods of making composite material leaf springs include, for example, filament winding methods, compression molding methods and pultrusion methods.
In the past, composite material leaf springs have been used in automotive vehicle suspension systems with associated hardware to accurately position and hold the spring. Such spring clamping hardware has been fashioned after hardware previously known for use in conjunction with metal leaf springs. In a typical arrangement, the spring is positioned between a clamping plate on one side and the axle or other wheel carrying member on the other side. Often, a second clamping plate or the like is positioned between the spring and the axle to act as a spring seat. Bolts or the like, for example U-bolts, are used to clamp the clamping plate and spring to the axle. An abrasion resistant pad can be used between the spring and the clamping plate and/or between the spring and the axle (or spring seat). Exemplary clamping hardware for a composite material leaf spring is seen, for example, in U.S. Pat. Nos. 3,968,958; 3,586,307 and 3,541,605.
Known leaf spring clamping hardware has been found inadequate in certain respects for use in conjunction with composite material leaf springs. Specifically, such spring clamping hardware has been found inadequate to hold the spring in a fixed position relative the axle under conditions experienced in ordinary use. More specifically, known spring clamping hardware has failed in ordinary use to prevent longitudinal movement of the spring, that is, movement of the spring in a direction along its longitudinal axis (which typically is transverse to the longitudinal axis of the axle). While the longitudinal position of the spring could be adequately fixed by providing a hole through the composite material of the leaf spring and bolting the spring to the spring clamping hardware, this presents several disadvantages. Providing the bolt hole in the leaf spring requires additional fabrication time and introduces additional complexity and cost. In addition, the bolt hole significantly weakens the composite material spring, and so the spring must be made larger, heavier and more costly.
Movement of the composite material leaf spring relative the axle or other wheel carrying member in a direction along the longitudinal axis of the leaf spring changes the pivot point of the leaf spring against the axle. Consequently, the spring rate is altered and the spring fails to perform according to design. Moreover, upon flexure of the spring, the compressive and tensile stresses are improperly distributed, which can lead to increased material fatigue and decreased spring life. Moreover, if excessive, such movement can lead to damage to the vehicle powertrain.
A composite material leaf spring suitable for use on an automotive vehicle and an axle clamp for use with same is disclosed in commonly assigned U.S. patent application Ser. No. 405,961 filed June 25, 1982. The composite material leaf spring comprises a position-setting concavity in its surface and the axle clamp comprises a corresponding position-setting convexity. Together, the position-setting concavity and the position-setting convexity accurately and securely fix the position of the composite spring relative the axle clamp and, indirectly, relative the axle. In one embodiment, a resilient sheet is positioned mediate the clamping plate and the leaf spring other than at the area of engagement of the position-setting concavity by the clamping plate channel convexity, and a resilient spring seat pad is positioned mediate the leaf spring and the axle or more typically mediate the leaf spring and a spring seat.
It is an object of the present invention to provide an axle clamp which secures a filament reinforced composite material leaf spring in position relative the axle. More particularly, it is an object of the invention to provide an axle clamp which in ordinary use substantially prevents longitudinal movement of the leaf spring, that is, movement of the spring in a direction along its longitudinal axis. Further, it is a particular object of the invention to provide an axle clamp which does not require either damage or dislocation of either the reinforcing filaments or the resin matrix of the leaf spring and, specifically, which does not require any hole(s) through the leaf spring or concavities in the surface of the leaf spring or other complexities in the shape of the leaf spring.